JP2611118B2 - Room temperature curing resin kit - Google Patents

Abstract

Foundry moulds or cores are made by a method comprising mixing a granular refractory material with a potassium alkali phenol-formaldehyde resin binder solution, forming the mixture and curing the formed mixture by gassing with a 1-3C alkyl formate. Cure by gassing with a formate, particularly methyl formate, enables rapid and efficient production of foundry moulds or cores. The formates used have relatively low toxicity.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a cold-setting resin kit which does not generate an irritating acid gas upon thermal decomposition.
Phenol-formaldehyde condensation products and phenol-formaldehyde / furfuryl alcohol condensation products obtained using strong acids such as sulfuric acid and p-toluenesulfonic acid as catalysts are used in the production of casting molds and the cores used in the production of the same core. It is well known as an agent. However, these condensation products have the disadvantage of producing a pungent odor of sulfur dioxide on thermal decomposition.

[0002] An alkaline phenol resin produced by using an ester as a catalyst is suggested in Japanese Patent Application Laid-Open No. 50-130,627, and is a pending Japanese Patent Application No. 803.
No. 1536 (Specification No. 2059972) and No. 8201668. The use of such a binder system does not generate irritating acid gas during mixing or casting. Furthermore, rapid curing at ambient temperature can be achieved by appropriate choice of resin and ester catalyst. However, obtaining such results on a large scale requires the use of certain rapid mixing devices such as those described in Baker Perkins UK Patents 1,257,181 and 1,369,445.

[0003] The present invention is based on the discovery that the use of esters as catalysts for alkaline phenolic resins is applicable to gas absorption processes which allow rapid curing at ambient temperature. It is known to use a gas absorption method to accelerate the curing of the casting mold and binder for the core. The main methods used or used industrially are as follows. a) "carbon dioxide method", in this way passed through a CO ₂ in a mixture of sand and sodium silicate. However, the resulting core or mold is very sensitive to water, loses its "dump back" strength during storage, does not accept rinsing, and has a low br
eak down) becomes very bad. It is necessary to add a spreading agent such as sucrose to promote good spreading. After gas absorption, the strength becomes very poor. b) "Sulfur dioxide method", UK Patent 1,411,975
This is the method taught by Sapic in the issue specification, which uses both of the following: (1) peroxides that are dangerous to store and handle, especially in a casting environment, and (2) have low threshold values (TLV) and are uncomfortable irritating to the touch. SO ₂ gas. c) "Isocuring", UK Patent 1,190,644
Ashland describes the use of benzylic ether phenolic polyols and methylene diphenyl diisocyanate. The reaction between the polyol and the diisocyanate is accelerated by gassing with triethylamine or dimethylethylamine. Diisocyanates have very low TLV values and react preferentially with water over polyols, so dry sand and dry to transfer a mixture of sand and binder into cores or flasks It is necessary to use air. The TLV values of amines are relatively low and their toxicology is not well understood. The cured core tends to absorb water and loses some of its strength on storage. Certain casting disadvantages are observed with "isocure" cores / molds. For example, the generation of pinholes caused by the nitrogen content of the binder. This nitrogen is reduced to ammonia in the casting environment, dissolved in the molten metal and gasified on cooling to small bubble cavities; the "defect of graphite", the deposition of graphite carbon, which The flakes collect on the surface and are "finned" (f
inning or "veinin"
g). This is caused by the mold or core under expansion stress during casting, and the molten metal instantaneously cracks.

[0004] The present invention makes it possible to produce a cured product quickly and efficiently without the inconvenience of the conventional method as described above. For example, it is possible to produce a casting mold or a core. 1) Granular refractory material is a), b) and c) a) weight average molecular weight (w) = 600-1500 b) molar ratio of formaldehyde: phenol = 1.2 :
1 to 2.6: 1 and c) KOH: phenol molar ratio = 0.2: 1 to 1.
Aqueous solution of potassium alkaline phenol-formaldehyde resin having 2: 1 properties (solids content 50-70
%) And 0.05 to 3 based on the weight of the resin solution.
Mixing with a binder containing at least one silane by weight; 2) shaping the mixture into a ventilated core or flask; 3) adding at least one formic acid to the shaped mixture. A step of absorbing the alkyl C ₁ -C ₃ gas to cure the binder. For example, when manufacturing casting molds or cores, the particulate refractory material is conventionally used in the foundry industry for casting molds and cores such as silica sand, chromite sand, zircon or olivine sand. Any of the materials may be
Difficulties commonly associated with caking alkaline-acting sands such as olivine sand, chromite sand and beach sand containing shell pieces (which can be due to neutralization or partial neutralization of the acid catalyst used) Although derived from the sum), the present invention has the particular advantage that it is completely overcome because the binder is cured under alkaline conditions. Therefore, the present invention is particularly useful where it is necessary or desirable to use alkaline sand.

[0005] The nature of the phenol-formaldehyde resin used forms an important feature of the present invention. There are several important characteristics of the resin. Since the present invention relates to a room temperature curing method, the resin binder is used as an aqueous solution of the resin. The solids content in this aqueous solution is in the range of 50-75% by weight. The reason for not using a solids content below 50% is that too much water reduces the effectiveness of the binder. Solids contents above 75% are not used because the viscosity of the aqueous solution is too high.

[0006] The phenol-formaldehyde resin used in the present invention has a weight average molecular weight (600 to 1500).
w). The strength of the products obtained using resins having w outside this range is relatively weak or slow growing. The inventors have to date used resins with w in the range of 700 to 1100 to obtain the best results. The resin used in the present invention is a potassium alkaline phenol-formaldehyde resin, which means that the alkali in the resin is potassium alkali.
The alkali may be added to the resin during the production of the resin, but it may also be added to the resin after the production, preferably as KOH at an appropriate concentration. The alkalinity of a resin is represented by its KOH content and, in particular, by the molar ratio of KOH to phenol in the resin. Other alkalis, such as NaOH, are not further excluded and may be present in small amounts, but are not particularly added, since they give low strength products.

The molar ratio of KOH: phenol in the resin solution is 0.2: 1 to 1.2: 1, preferably 0.3: 1 to 1: 1.
It is in the range of 1: 1. Outside this range the strength of the product is relatively poor and above the upper limit it is dangerously alkaline. We believe that the molar ratio of KOH: phenol is 0.4
Even with low amounts of silane, as low as 0.05% by weight, based on the weight of the resin solution, using a resin solution that is in the range of ０．６0.6 significantly improves the strength. The amount of silane is about 0.6 based on the same standard.
The strength is greatly improved when increasing to weight percent. High concentrations of silane are not preferred because they add cost. Furthermore, since the silanes typically used are nitrogen-containing gamma-aminopropyltriethoxysilanes, the use of an excess of silanes may increase the risk of causing pin pole defects. For these reasons 3% by weight of the resin solution
No amount of silane above is used.

[0008] When producing a casting mold or core, the binder and the particulate refractory material can be mixed and molded by conventional methods. The well ventilated core and flask used can also be of the conventional type as used in conventional gas removal methods. According to the invention, the binder has best results in absorbing alkyl formate C ₁ -C ₃ , and very preferably methyl formate.

The resins used are 1.2: 1 to 2.6:
Although it has a formaldehyde: phenol molar ratio of 1, preferably 1.5: 1 to 2.2: 1, a molar ratio lower than this range is not used because at such a molar ratio the resin It is not relatively reactive. On the other hand, molar ratios higher than this range are also not used because the resulting resin contains undesirably high levels of unreacted formaldehyde and gives low strength products.

It is a secondary aspect of the present invention that the resin used satisfies the following criteria: a) w = 700-1100 b) KOH: phenol molar ratio = 0.4-0.6 and c) formaldehyde: phenol molar ratio = 1.5:
It is cured by increasing the strength by including a 1-2. 2: 1 silane in the binder. The alkyl formate curing catalyst is not usually used as a pure gas, but as a vapor or aerosol in an inert carrier gas. Here, the inert carrier gas means a gas that does not react with the formate catalyst or a gas that adversely affects the properties of the curing reaction or the product. Suitable examples include air, nitrogen or carbon dioxide.

The supplied catalyst is an alkyl formate C ₁ -C ₃
And preferably dispersed in the carrier gas as a vapor or as an aerosol. Other esters, such as formic acid esters such as formic acid butyl of higher alcohols, and C ₁ -C ₃ esters such as methyl acetate or the ethyl and alcohols with lower carboxylic acids are not effective as a gas catalyst fed. As a catalyst, methyl formate is more active than ethyl formate, and ethyl formate is better than propyl formate. It is not clear why the catalytic activity of alkyl formate C ₁ -C ₃ as well as why methyl formate is outstandingly outstanding in this group. The relatively volatility of these compounds allows them to be absorbed catalysts. This is 31.5 ° C at normal pressure
This is especially true for methyl formate, which is a volatile liquid having a boiling point of. At ambient temperature (up to 31.5 ° C.), typically at 15-25 ° C., methyl formate is sufficiently volatile that carrier gas is passed through methyl formate (maintained at ambient temperature) The concentration of methyl formate in the gas is such that the catalyst acts to cure the binder.
Ethyl and propyl formate, which have boiling points in the range of 54-82 ° C at normal pressure, are less volatile than methyl esters. To transfer sufficient amounts of these esters into the gas phase to make them effective catalysts, it is necessary to heat the esters to near their boiling point and use a stream of carrier gas heated to, for example, 100 ° C. It has been found suitable.

An alternative to true evaporation is to create an aerosol in the carrier gas. Methyl formate is too volatile to make it impractical. In using ethyl formate and propyl formate, it is desirable to preheat the ester or the like while absorbing them into the core or template to increase the degree of dispersion in the core or template.

As mentioned above, methyl formate is the most active catalyst and its easiest to use because of its volatility. Thus, the use of methyl formate in a stream of inert carrier gas as a catalyst to be absorbed is a unique aspect of the present invention. A further practical advantage of these formates, especially methyl formate, is that their toxicity is relatively low and their toxicity is well understood.

The concentration of the formate catalyst in the carrier gas is preferably at least 0.2% by volume, typically from 0.5 to 5% by volume. The total amount of catalyst used will depend on the particular conditions used, but will typically be from 5 to 60% by weight, preferably from 15 to 60% by weight, based on the weight of the resin solution.
35% by weight. The time required for successful absorption depends on the size and complexity of the core or mold and the particular resin used. It can be as short as 0.1 second, but more usually is in the range of 1 second to 1 minute. Longer times, for example up to 5 minutes, can also be used if necessary or in the case of large molds or cores. After absorption, remove the core or mold from the frame. Sufficient time must elapse to increase the strength of the mold and core so that the mold and core can be removed from the frame without damage. Production rates can be increased by washing the mold or core with a suitable inert gas such as air to remove residual catalyst vapor and moisture and other by-products of the curing reaction.

The amount of the resin solution used as the binder is 0.5 to 8% by weight, preferably 1 to 3% by weight, based on the weight of the fine refractory material. Using less binder results in poor core strength. There is no great advantage even if it is used more, and breakage at the time of pouring (break)
down) and the difficulty of collecting sand increases. The following examples illustrate the invention, but the techniques used in the examples will first be described. Preparation of Phenol-Formaldehyde Resin Solution 100% phenol is mixed with 50% phenol to form an amount corresponding to the desired KOH: phenol molar ratio (0.2-1.2).
Dissolve in KOH aqueous solution. The solution was heated to reflux and a 50% aqueous formaldehyde solution was gradually added in an amount corresponding to the desired formaldehyde: phenol molar ratio (1.6, 1.8 or 2.0) while continuing to reflux. The reflux of the reaction mixture was continued until the viscosity of the reaction mixture reached a predetermined viscosity corresponding to the desired value of w (the solids content can be adjusted by distillation if desired, but this is usually not necessary. This has the following advantages of the present invention: a small amount of KOH solution may be added to adjust the KOH: phenol ratio, but may not be necessary for large-scale production). The resin solution was cooled to 40 ° C. and 0.4% by weight, based on the weight of the resin solution, of γ-aminopropyltriethoxysilane was added.

Resin test a) Viscosity: 25 ° C. using an Ostwald (U-tube) viscometer
Was measured. b) Fixed volume: weighed sample (2.0 ±
0.1 g) was heated to 100 ° C. for 3 hours. c) Weight average molecular weight: gel permeation chromatography (G
(PC) and the molecular weight was determined by calibration with a phenolic resin standard sample. The GPC peak position (Ve) is determined by two internal standards, nitrogen (Vi) and very high molecular weight polystyrene (V
(V) represented by the distribution coefficient K calculated for (o)
Extreme values of i and Vo elution volumes. ).

Embedded image Since the peak position of Vi (nitrogen) is close to infinity and the peak position of Vo (high molecular weight polystyrene) is close to 0, V
It can be said that i and Vo are negligible and K is almost proportional to Ve. That is, the value of K can be obtained by measuring Ve. The K value of various compounds can be found in JOURNAL OF APPLIED POLYMER SCIENCE, Vol. 16, pp. 1585-1602 (1972), published in 1972.
The relationship between K and molecular size (ie, molecular weight) is shown in Table II on page 1 of FIG. 1. In the bottom row of Table II, K having a molecular weight of 1700 is 0.1
39, which is shown in FIG. 1 is plotted. Table II lists the K values for various phenolic standards. Therefore, for polymers of unknown molecular weight, K
When the values are measured, FIG. The molecular weight can be known from 1.

Preparation of Sand Core Mixture for Casting The selected sand was placed in a Fordath laboratory core mixer and mixed with the phenol-formaldehyde resin prepared as described above for 2 minutes. The mixture was discharged into a tin and sealed immediately to prevent evaporation of water.

Production of Test Casting Core B. F. Working Party (Working
5 × 5 cm cylinder compression specimens were prepared by the standard method recommended by Party P, but using a perforated bottom plate in a cylinder having a recess that could be connected to a negative pressure source. The top of the cylinder was sealed with another perforated plate connected to a bubbler containing liquid methyl formate at ambient temperature. Applying a vacuum to the bottom plate causes air to bubble through the methyl formate and the ester vapors in the air stream move through the sand-resin mixture in the cylinder core. The obtained core was subjected to 1 minute, 5 minutes, 1 hour, 2 hours, 3 hours and 2 hours at 20 ° C. and 50% relative humidity.
After storing for 4 hours, the compressive strength was measured. Initial tests have shown that 30 seconds is sufficient time to obtain optimal strength. This time was used as a standard time in the following examples.

Example 1 A core was produced by using a resin solution having the following properties and adding 0.4% by weight of γ-aminopropyltriethoxysilane based on the resin solution. Formaldehyde: phenol molar ratio 2.0 KOH: phenol molar ratio 0.4-
0.8 w 960 or 1000 solids content 63.5% The sand used was Chelford 50 and the resin content was 25% by weight based on the weight of the sand. The test results are listed in Tables 1 and 2. Table 1 shows the test results when a resin with w = 960 was used, and Table 2 shows the results when a resin with w = 1000 was used. From the data in the table, it can be seen that a core having a suitable strength can be produced, however, the strength is slightly reduced when the molar ratio of KOH: phenol is larger than 0.6.

[0020]

[0021]

Example 2 A test core was produced using a resin solution having the following properties. Formaldehyde: phenol molar ratio 2.0 KOH: phenol molar ratio 0.65 w 718-1050 Solids content 66% 0.4% by weight of γ-aminopropyltriethoxysilane was added to the resin solution. The sand used is Chelford 50
And the amount of resin solution used was 2% by weight based on the weight of the sand. The experiment was repeated using a similar solution to which a 50% KOH solution was added to increase the molar ratio of KOH: phenol to 0.85. The solids content of the resin solution was 64%. The test results are listed in Table 3. Data when using a resin having a molar ratio of KOH: phenol = 0.65 is shown in column (a), and data when using a resin having a molar ratio of KOH: phenol = 0.85 is shown in column (b). Column. Example 1
As described in U.S. Pat. No. 5,838,838, the use of a resin with a high molar ratio of KOH: phenol gives poor results, especially at higher w values.

[0023]

Example 3 Test cores were produced as described above using resins having different properties. The sand used was Chelford 50, the amount of resin solution was 2% by weight based on the weight of the sand,
And all resin solutions contained 0.4% by weight of γ-aminopropyltriethoxysilane. The test results are listed in Table 4.

[0025]

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Jeffrey Davids Railton, UK Southampton, Shearley, Wollen, Bracken Lane 12 (72) Inventor Peter Raymond Ladrum, UK Hampshire Yard, N.R.M. (72) Inventor, Timassy Jillon Reynolds, United Kingdom Southampton, Shearley, Percy Road

Claims (8)

(57) [Claims] 1. A cold curing resin kit comprising (A) a binder and (B) a curing agent as separated components,
The binder (A) comprises: (1) an aqueous solution of the following potassium alkaline phenol formaldehyde resin, i) its solid content 50 to 75% ii) the weight average molecular weight (w) of the resin: 600 to 150
0 iii) Formaldehyde: phenol molar ratio = 1.2: 1 to 2.6: 1 iv) Resin KOH: phenol molar ratio = 0.2: 1
1.2: 1 (2) At least one silane of 0.05 to 3% by weight based on the weight of the aqueous resin solution, wherein the curing agent (B) is dispersed in the carrier gas as vapor or aerosol. A cold-setting resin kit comprising C ₁ -C ₃ alkyl formate. 2. A resin having a weight average molecular weight w of 700 to 1
The kit according to claim 1, which is 100. 3. The molar ratio of KOH: phenol is 0.3:
The kit according to claim 1, wherein the ratio is 1 to 1: 1. 4. The molar ratio of KOH: phenol is 0.4:
The kit according to claim 2 or 3, wherein the ratio is 1 to 0.6: 1. 5. The kit according to claim 1, wherein the molar ratio of formaldehyde: phenol is from 1.5: 1 to 2.2: 1. 6. The kit according to claim 4, wherein the molar ratio of formaldehyde: phenol is from 1.5: 1 to 2.2: 1. 7. The method according to claim 1, wherein the binder is 1% based on the weight of the aqueous resin solution.
5-35% by weight formic acid _C 1 -C ₃ kit of claim 1 wherein which can be cured in contact with an alkyl. 8. The kit according to claim 1, wherein the C ₁ -C ₃ alkyl formate is methyl formate.